Redirect unauthorized resque-web polling requests to root url 

This is the v2 version of https://github.com/defunkt/resque/pull/826, which fixes a minor annoyance that I've come across within resque-web:

If I'm polling resque-web in one tab and then impersonate a user that doesn't have access to resque-web in another tab, my logs get flooded with unauthorized requests. Instead of continuing the polling in that case, I think it would be better to redirect elsewhere.